There is a demand for effectively utilizing image content by enabling image content with the spread of an information communication technology to be viewed under a condition different from a condition when created. For example, in an Internet protocol television (IPTV) or the like, there are cases in which image content (a so-called network moving image) of relatively low resolution that is originally created to be viewed through a mobile terminal device or the like is displayed on an image display device of high resolution. Here, image content having resolution of 640 pixels (a horizontal direction)×360 pixels (a vertical direction) is displayed on a display that supports a full high definition (HD) standard of 1920 pixels (the horizontal direction)×1080 pixels (the vertical direction). In this case, resolution may be converted into high resolution by interpolating a signal value of each pixel included in image content between pixels (this is also referred to as up-scaling or up-convert).
There are cases in which the following noises are remarkably shown in an image whose resolution is increased:
(1) jaggy: a step-like contour shown in a slant line or a curved line;
(2) mosquito noise: wave-like noise shown in a portion in which a contrasting density or color signal value abruptly changes or its vicinity when a compression-coded code is decoded; and
(3) dot interference: noise shown in a granular form in a boundary in which a color changes when separation (YC separation) of a brightness signal and a color-difference signal from a composite signal is inappropriate.
In this regard, in the past, an attempt to cause a signal value interpolated into an image having an increased resolution to be subject to a low pass filter and reduce noise has been made. For example, in a processing device disclosed in JP 2005-353068 A, a window of a certain size is set on an input current frame/field based on a current pixel, an eigenvalue and an eigenvector used to determine characteristics of the window are calculated, the characteristics of the window are determined based on the calculated eigenvalue, a filtering weighted value to be applied is decided based on the determination result, and filtering is performed on the window based on the calculated eigenvector and the decided filtering weighted value.
In addition, an attempt to perform image sharpening (which is also referred to as “emphasis/enhancement”) by emphasizing information of a high frequency component of an interpolated signal value has been made.
Further, an image processing device that performs image conversion according to a type of a broadcast wave of video has been proposed. For example, an image processing device disclosed in JP 2010-93856 A includes an image converting unit that converts a first video signal having first resolution into a second video signal having second resolution higher than the first resolution according to a parameter indicating a ratio of pixels of a high frequency component to be inserted into pixels of the first video signal and a control unit that performs control such that the parameter is changed according to a type of a broadcast wave of the first video signal.